A cove molding has a concave-profile and is often used at the junction of an interior wall and ceiling, on furniture, and for picture frames for art, though it is often used as a design element in various other applications. Because of its elegant look, cove molding is a favorite of architectural and other professional designers. However, the prior art methods of making a cove molding on a table saw requires complicated, and sometimes unsafe, set-ups which are difficult to reproduce if additional molding is needed at a later time. The most common prior art method involves clamping a board or other straight-edged material to the table saw with the blade raised to the cove final cut height and adjusting this fence's location by trial and error. The saw blade is then lowered to just above the saw table surface. Using the auxiliary fence to position the molding blank, the cove is formed by making multiple passes of the molding blank over the saw blade, each time raising the blade approximately 1/16″ until the final cove depth and width are achieved. In actual practice, the first problem encountered is the structure of the underside of a saw's table casting. Either it is cast as a ribbed item, or it may be cast with other features that impede secure clamping of the fence. Also, clamping at the front of the saw table must accommodate the variation from the top of the saw table to the top of the fence guide rail which is lower than the table top. Many older table saws use a round bar as the fence guide rail, which further complicates clamping by requiring a V-block and other fixturing. The back of many saw tables has little or no area sufficient for solid clamping of the trailing edge of the temporary fence. Also, any adjustment of the fence requires re-setting the clamping, blocking, and shimming at both the front and the back of the saw table.
To cut an open cove molding, where the cove is cut only on the front portion of the blade, involves a cumbersome process requiring lowering the blade, placing the fence above the blade, turning the saw on, raising the blade to the height of the cove cut, cutting through the fence in the process, and performing a test cove run. If further adjustment is required, all the steps must be repeated for each adjustment, and with each adjustment another cut is introduced to the fence. This cumbersome, time consuming process discourages most woodworkers. Additionally, reproducing a previously produced molding in the future requires going through all the above steps again.
Jigs utilizing a parallelogram design for producing straight housed coves of limited width and depth are commercially available. Within this narrow range such jigs perform reasonably well, but often in architectural and furniture crafts, open and housed profiles are required in a flat and vertical orientation, and often require matching inside and outside curved profiles in both horizontal and vertical orientations. Such commercially available jigs are not able to produce such coves. To achieve these alternative coves even in large industrial shops requires many different machines and specialized tooling, thus making them expensive and impractical.